It is well known that extremely high voltages can develop in the vicinity of an integrated circuit due to the build-up of static charges. A high potential may be generated to an input or output buffer of an integrated circuit, which may be caused by a person touching a package pin that is electrically connected to the input or output buffer. When the electrostatic charges are discharged, a high current is produced at the input and output nodes of the integrated circuit. Electrostatic discharge (ESD) is a serious problem for semiconductor devices since it has the potential of destroying the entire integrated circuit.
The duration of the ESD transient is very short, typically in the order of nanoseconds, and the conventional circuit breakers cannot react quickly enough to provide adequate protection. For this reason, it has become a known practice to incorporate ESD devices in integrated circuits, and/or to add features to improve the self-protection ability of integrated circuit devices against ESD.